A standard drill chuck has a body element centered on and rotatable about an axis and formed centered on the axis with a rearwardly open spindle hole and a forwardly open tool hole. A ring element is axially fixed but rotatable about the axis on the body element. One of the elements is formed with a plurality of angled guide passages opening axially forward into the tool hole and the other of the elements is formed centered on the axis with a screwthread exposed in the passages. Respective jaws axially and radially displaceable in the passages are each formed with a row of teeth meshing with the screwthread so that rotation of the ring element in one direction displaces the jaws toward one another and opposite rotation displaces them away from one another.
German patent 3,437,792 of G. H. Rohm describes such a system where the actual tool-engaging jaws ride on angled surfaces of the chuck body and are pushed along them by actuating elements that only move axially in the chuck body. The ring element is formed with the screwthread and can be rotated by means of a key.
So-called keyless systems are known from commonly owned U.S. Pat. Nos. 5,236,206 and 5,829,761 which have a knurled sleeve either itself formed with the guide passages or connected to the ring. They are very convenient to use, eliminating the need for a separate key to open and close the chuck.
In all such systems the structure of the chuck body at least is expensive to manufacture. It is invariably made of steel and must be machined in several different stages so that the various holes and passages all have the proper dimensions. The passages must be drilled out so that jaws with round shafts are used, creating a problem of the jaws wanting to rotate in the passages when torsionally stressed during a drilling operation.